The present invention relates to the field of crystal monochromators, and more particularly to crystal monochromators for providing a monochromatic x-ray wavelength.
In the art of monochromators, a number of techniques are known to provide a monochromatic wavelength.
In U.S. Pat. No. 3,772,522, a crystal monochromator for x-rays is disclosed which employs a spherically bendable quartz disc rigidly attached to a spherically shaped rigid quartz substrate to form a diffraction element. The x-ray source, the diffraction element, and a single target are arrayed on a circular array known as a Rowland circle. With this device, plural monochromatic x-ray beams are not provided, and the rigid diffraction element is not capable of being bent in order to focus the x-ray beam on the target.
In U.S. Pat. No. 4,737,973, in the discussion of the background of the invention, there is a disclosure that silicon or germanium crystal material can be sliced to a thickness of several millimeters or less, and stress is applied from the two ends of the slice to focus a single diffracted x-ray beam. There is no disclosure of providing plural monochromatic x-ray beams with the bent crystals that are disclosed. The patented device itself is for a crystal monochromator having a base crystal layer and a plurality of crystal layers stacked on the base crystal layer, where the upper crystal layer of the stack has a larger spacing of lattice plane than that of each lower crystal layer of the crystal stack. This complex device is for focussing a divergent source beam onto a single focal point. This device is not disclosed for providing plural monochromatic beams.
In U.S. Pat. No. 4,675,889, a disclosure is made of a multiple wavelength x-ray dispersive device that can receive an x-ray beam containing a plurality of x-ray wavelengths and provide a plurality of separated x-ray wavelengths at the same or different angles. The dispersive device is comprised of a plurality of vertically stacked layer sets of two parallel layers each. The layers are parallel to the top layer of the vertical stack. The first layer in each set has a first interplanar spacing which provides x-ray diffraction properties at a first wavelength. The second layer in each layer set has a parallel second, and larger, interplanar spacing which provides x-ray diffraction properties at a second wavelength. A large number (20-100) of alternating first sets and second sets are provided. In view of the above, it would be desirable to provide a simple, multiple wavelength x-ray dispersive device that does not require a large number of repeating layered units.
U.S. Pat. No. 4,675,899 also discloses that commercial x-ray dispersive structures are formed from crystalline structures such as LiF, metal acid phthalates (map), pyrolytic graphite, and Langmuir-Blodgett (LB) films. However, there does not appear to be a utilization of crystalline properties of the layered material. For example, nothing in this patent discloses a first set of crystal planes parallel to the top surface along with a second set of crystal planes inclined at an angle of inclination with respect to the top surface.
U.S. Pat. No. 4,649,557 discloses an x-ray analysis apparatus which includes a doubly curved monochromator crystal having doubly curved crystal lattice surfaces, so that the monochromator crystal exhibits mutually and significantly different amounts of surface curvature in different principal directions. With this device, plural monochromatic x-ray beams are not provided.